What Is HACL?

The HACL for Java™ is a set of classes and methods that allow application programmers to access host applications at the 3270 and 5250 data stream levels easily and quickly. HACL implements the core host access function in a complete class model that is independent of any graphical display and only requires a Java-enabled browser or comparable Java™ environment to operate.

The class library represents a complete object-oriented abstraction of a host connection, including:
  • Reading and writing the host presentation space (screen)
  • Enumerating the fields in the presentation space
  • Reading the operator information area (OIA) for status information
  • Transferring files
  • Performing asynchronous notification of significant events

Application programmers can write Java™ applets that manipulate data from the data stream presentation space (such as 3270 and 5250) without requiring applets to reside on these machines. The presentation space represents an imaginary terminal screen that contains both data and associated attributes presented by host applications. After an interaction is complete, the applet can switch to other tasks or simply close the session. The transaction can be completed without ever showing host screens.

HACL Java™ applets can:
  • Open a session to the host
  • Wait for incoming host data
  • Get specific strings from the imaginary screen
  • Get associated attributes of the strings
  • Set new string values
  • Send data stream function keys back to the host
  • Wait for the next host session
HACL is a significant improvement over client-specific, screen scraping application programming interfaces like EHLLAPI in several ways, such as:
  • HACL is platform independent
  • HACL operates directly on the data stream rather than on the interpreted emulator screen. This eliminates the overhead of interpreting and displaying the datastream in a visual window.
  • HACL does not require emulator software running on the local workstation, reducing dependencies on platform-specific screen formats and keyboard layouts.
  • HACL is downloadable and executable on client workstations using standard Web and Java™ technology. This provides significant maintenance and resource savings.